Silicon-based energy storage devices with ether containing electrolyte additives

ABSTRACT

Electrolytes and electrolyte additives for energy storage devices comprising an ether compound are disclosed. The energy storage device comprises a first electrode and a second electrode, wherein at least one of the first electrode and the second electrode is a Si-based electrode, a separator between the first electrode and the second electrode, an electrolyte, and at least one electrolyte additive selected from ether compounds.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of U.S.application Ser. No. 16/989,510, filed Aug. 10, 2020, pending (nowallowed), which is a continuation of and claims the benefit of U.S.application Ser. No. 16/213,944, filed Dec. 7, 2018, issued (now U.S.Pat. No. 10,811,727), which claims the benefit of U.S. ProvisionalApplication No. 62/596,044, filed Dec. 7, 2017. The entirety of each ofthe above referenced applications is hereby incorporated by reference.

BACKGROUND Field

The present application relates generally to electrolytes for energystorage devices. In particular, the present application relates toelectrolytes and additives for use in lithium-ion energy storage deviceswith silicon-based anode materials.

Description of the Related Art

As the demands for both zero-emission electric vehicles and grid-basedenergy storage systems increase, lower costs and improvements in energydensity, power density, and safety of lithium (Li)-ion batteries arehighly desirable. Enabling the high energy density and safety of Li-ionbatteries requires the development of high-capacity, and high-voltagecathodes, high-capacity anodes and accordingly functional electrolyteswith high voltage stability, interfacial compatibility with electrodesand safety.

A lithium-ion battery typically includes a separator and/or electrolytebetween an anode and a cathode. In one class of batteries, theseparator, cathode and anode materials are individually formed intosheets or films. Sheets of the cathode, separator and anode aresubsequently stacked or rolled with the separator separating the cathodeand anode (e.g., electrodes) to form the battery. Typical electrodesinclude electro-chemically active material layers on electricallyconductive metals (e.g., aluminum and copper). Films can be rolled orcut into pieces which are then layered into stacks. The stacks are ofalternating electro-chemically active materials with the separatorbetween them.

Si is one of the most promising anode materials for Li-ion batteries dueto its high specific gravimetric and volumetric capacity (3579 mAh/g and2194 mAh/cm³ vs. 372 mAh/g and 719 mAh/cm³ for graphite), and lowlithiation potential (<0.4 V vs. Li/Li⁺). Among the various cathodespresently available, layered lithium transition-metal oxides such asNi-rich Li[Ni_(x)Co_(y)Mn(Al)_(1−x−y)]O2 (NCM or NCA) are the mostpromising ones due to their high theoretical capacity (˜280 mAh/g) andrelatively high average operating potential (3.6 V vs Li/Li⁺). CouplingSi anodes with high-voltage Ni rich NCM (or NCA) cathodes can delivermore energy than conventional Li-ion batteries with graphite-basedanodes, due to the high capacity of these new electrodes. However, bothSi-based anodes and high-voltage Ni rich NCM (or NCA) cathodes faceformidable technological challenges, and long-term cycling stabilitywith high-Si anodes paired with NCM or NCA cathodes has yet to beachieved.

For anodes, silicon-based materials can provide significant improvementin energy density. However, the large volumetric expansion (>300%)during the Li alloying/dealloying processes can lead to disintegrationof the active material and the loss of electrical conduction paths,thereby reducing the cycling life of the battery. In addition, anunstable solid electrolyte interphase (SEI) layer can develop on thesurface of the cycled anodes, and leads to an endless exposure of Siparticle surfaces to the liquid electrolyte. This results in anirreversible capacity loss at each cycle due to the reduction at the lowpotential where the liquid electrolyte reacts with the exposed surfaceof the Si anode. In addition, oxidative instability of the conventionalnon-aqueous electrolyte takes place at voltages beyond 4.5 V, which canlead to accelerated decay of cycling performance. Because of thegenerally inferior cycle life of Si compared to graphite, only a smallamount of Si or Si alloy is used in conventional anode materials.

The NCM (or NCA) cathode usually suffers from an inferior stability anda low capacity retention at a high cut-off potential. The reasons can beascribed to the unstable surface layer's gradual exfoliation, thecontinuous electrolyte decomposition, and the transition metal iondissolution into electrolyte solution. In order to make good use of Sianode//NCM or NCA cathode-based Li-ion battery systems, theaforementioned barriers need to be overcome.

One strategy for overcoming these barriers includes exploring newelectrolyte additives in order to make good use of Si anode//NCM or NCAcathode-based full cells. The next generation of electrolyte additivesto be developed should be able to form a uniform, stable SEI layer onthe surface of Si anodes. This layer should have low impedance and beelectronically insulating, but ionically conductive to Li-ion.Additionally, the SEI layer formed by the additive should have excellentelasticity and mechanical strength to overcome the problem of expansionand shrinkage of the Si anode volume. On the cathode side, the idealadditives should be oxidized preferentially to the solvent molecule inthe bare electrolyte, resulting in a protective cathode electrolyteinterphase (CEI) film formed on the surface of the NCM (or NCA). At thesame time, it should help alleviate the dissolution phenomenon oftransition metal ions and decrease surface resistance on cathode side.In addition, they could help improve the physical properties of theelectrolyte such as ionic conductivity, viscosity, and wettability.

SUMMARY

In some aspects, energy storage devices are provided. In someembodiments, the energy storage device includes a first electrode and asecond electrode, wherein at least one of the first electrode and thesecond electrode is a Si-based electrode. In some embodiments, theenergy storage device includes a separator between the first electrodeand the second electrode. In some embodiments, the energy storage deviceincludes an electrolyte. In some embodiments, the energy storage deviceincludes at least one electrolyte additive comprising an ether compound.

In some embodiments, the energy storage device includes at least oneelectrolyte additive comprising a compound selected from Formulae (A),(B), (C), and (D):

wherein R₁ and R₂ are each independently selected from C1-C6 alkyl,C1-C8 heteroalkly with at least one heteroatom O, C2-C6 alkenyl,alkynyl, C2-C12 heteroalkenly with at least one heteroatom O; R₃, R₄,R₅, R₆, R₇, R₈, R₉, R₁₀, R₁₁, R₁₂, R₁₃, R₁₄, and R₁₅ are eachindependently selected from C2-C4 alkenyl; A, B, C, and D are eachindependently C1-C6 alkyl; and

In some embodiments, the second electrode is a Si-dominant electrode. Insome embodiments, the second electrode comprises a self-supportingcomposite material film. In some embodiments, the composite materialfilm comprises greater than 0% and less than about 90% by weight ofsilicon particles, and greater than 0% and less than about 90% by weightof one or more types of carbon phases, wherein at least one of the oneor more types of carbon phases is a substantially continuous phase thatholds the composite material film together such that the siliconparticles are distributed throughout the composite material film.

In some embodiments, the electrolyte further comprises fluoroethylenecarbonate (FEC). In some embodiments, the electrolyte is substantiallyfree of non-fluorine containing cyclic carbonate.

In some embodiments, the electrolyte additive is selected from the groupconsisting of allyl ether; 1,1,2,2-tetrafluoroethyl2,2,3,3-tetrafluoropropyl ether; 1-(2-methoxyethoxy)butane;2,5,8,11-tetraoxadodecane; 2,5,8,11,14-pentaoxapentadecane;3-(prop-2-enoxymethoxy)prop-1-ene; Ethylene glycol diallyl ether;1,4-Butanediol divinyl ether; Tri(ethylene glycol) divinyl ether;Di(ethylene glycol) divinyl ether; Triallyl orthoformate;1,2,3-tris(prop-2-enoxy)propane; Pentaerythritol Triallyl Ether,1-prop-2-enoxy-2,2-bis(prop-2-enoxymethyl)butane;1,3-bis(prop-2-enoxy)-2,2-bis(prop-2-enoxymethyl)propane;Tetrakis(vinyloxymethyl)methane;Bis[3-prop-2-enoxy-2,2-bis(prop-2-enoxymethyl)propyl] but-2-enedioate;and Glyoxal bis(diallyl acetal); 1,1,3,3-Tetraallyloxypropane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a cross-sectional schematic diagram of an example of alithium-ion battery 300 implemented as a pouch cell.

FIGS. 2A and 2B show the Capacity (A) and capacity retention ofSi-dominant anode//LiCoO₂ cathode full cells, respectively.

FIGS. 3A and 3B show average resistance during 10 sec pulse for thecharge (A) and discharge (B) processes of Si-dominant anode//LiCoO₂cathode full cell, respectively.

FIGS. 4A and 4B show average resistance during 30 sec pulses for thecharge (A) and discharge (B) processes of Si-dominant anode//LiCoO₂cathode full cells, respectively.

FIGS. 5A and 5B show the Capacity (A) and capacity retention ofSi-dominant anode//LiCoO₂ cathode full cells, respectively.

DETAILED DESCRIPTION Definitions

The term “alkyl” refers to a straight or branched, saturated, aliphaticradical having the number of carbon atoms indicated. The alkyl moietymay be branched or straight chain. For example, C1-C6 alkyl includes,but is not limited to, methyl, ethyl, propyl, isopropyl, butyl,isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, hexyl, etc. Otheralkyl groups include, but are not limited to heptyl, octyl, nonyl,decyl, etc. Alkyl can include any number of carbons, such as 1-2, 1-3,1-4, 1-5, 1-6, 1-7, 1-8, 1-9, 1-10, 1-11, 1-12 2-3, 2-4, 2-5, 2-6, 3-4,3-5, 3-6, 4-5, 4-6 and 5-6. The alkyl group is typically monovalent, butcan be divalent, such as when the alkyl group links two moietiestogether.

The term “fluoro-alkyl” refers to an alkyl group where one, some, or allhydrogen atoms have been replaced by fluorine.

The term “alkylene” refers to an alkyl group, as defined above, linkingat least two other groups, i.e., a divalent hydrocarbon radical. The twomoieties linked to the alkylene can be linked to the same atom ordifferent atoms of the alkylene. For instance, a straight chain alkylenecan be the bivalent radical of —(CH₂)_(n)—, where n is 1, 2, 3, 4, 5, 6,7, 8, 9, or 10. Alkylene groups include, but are not limited to,methylene, ethylene, propylene, isopropylene, butylene, isobutylene,sec-butylene, pentylene and hexylene.

The term “alkoxy” refers to alkyl group having an oxygen atom thateither connects the alkoxy group to the point of attachment or is linkedto two carbons of the alkoxy group. Alkoxy groups include, for example,methoxy, ethoxy, propoxy, iso-propoxy, butoxy, 2-butoxy, iso-butoxy,sec-butoxy, tert-butoxy, pentoxy, hexoxy, etc. The alkoxy groups can befurther substituted with a variety of substituents described within. Forexample, the alkoxy groups can be substituted with halogens to form a“halo-alkoxy” group, or substituted with fluorine to form a“fluoro-alkoxy” group.

The term “alkenyl” refers to either a straight chain or branchedhydrocarbon of 2 to 6 carbon atoms, having at least one double bond.Examples of alkenyl groups include, but are not limited to, vinyl,propenyl, isopropenyl, 1-butenyl, 2-butenyl, isobutenyl, butadienyl,1-pentenyl, 2-pentenyl, isopentenyl, 1,3-pentadienyl, 1,4-pentadienyl,1-hexenyl, 2-hexenyl, 3-hexenyl, 1,3-hexadienyl, 1,4-hexadienyl,1,5-hexadienyl, 2,4-hexadienyl, or 1,3,5-hexatrienyl. Alkenyl groups canalso have from 2 to 3, 2 to 4, 2 to 5, 3 to 4, 3 to 5, 3 to 6, 4 to 5, 4to 6 and 5 to 6 carbons. The alkenyl group is typically monovalent, butcan be divalent, such as when the alkenyl group links two moietiestogether.

The term “alkenylene” refers to an alkenyl group, as defined above,linking at least two other groups, i.e., a divalent hydrocarbon radical.The two moieties linked to the alkenylene can be linked to the same atomor different atoms of the alkenylene. Alkenylene groups include, but arenot limited to, ethenylene, propenylene, isopropenylene, butenylene,isobutenylene, sec-butenylene, pentenylene and hexenylene.

The term “alkynyl” refers to either a straight chain or branchedhydrocarbon of 2 to 6 carbon atoms, having at least one triple bond.Examples of alkynyl groups include, but are not limited to, acetylenyl,propynyl, 1-butynyl, 2-butynyl, isobutynyl, sec-butynyl, butadiynyl,1-pentynyl, 2-pentynyl, isopentynyl, 1,3-pentadiynyl, 1,4-pentadiynyl,1-hexynyl, 2-hexynyl, 3-hexynyl, 1,3-hexadiynyl, 1,4-hexadiynyl,1,5-hexadiynyl, 2,4-hexadiynyl, or 1,3,5-hexatriynyl. Alkynyl groups canalso have from 2 to 3, 2 to 4, 2 to 5, 3 to 4, 3 to 5, 3 to 6, 4 to 5, 4to 6 and 5 to 6 carbons. The alkynyl group is typically monovalent, butcan be divalent, such as when the alkynyl group links two moietiestogether.

The term “alkynylene” refers to an alkynyl group, as defined above,linking at least two other groups, i.e., a divalent hydrocarbon radical.The two moieties linked to the alkynylene can be linked to the same atomor different atoms of the alkynylene. Alkynylene groups include, but arenot limited to, ethynylene, propynylene, butynylene, sec-butynylene,pentynylene and hexynylene.

The term “cycloalkyl” refers to a saturated or partially unsaturated,monocyclic, fused bicyclic, bridged polycyclic, or spiro ring assemblycontaining from 3 to 12, from 3 to 10, or from 3 to 7 ring atoms, or thenumber of atoms indicated. Monocyclic rings include, for example,cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and cyclooctyl.Bicyclic and polycyclic rings include, for example, norbornane,decahydronaphthalene and adamantane. For example, C3-C8 cycloalkylincludes cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclooctyl,and norbornane. As used herein, the term “fused” refers to two ringswhich have two atoms and one bond in common. For example, in thefollowing structure, rings A and B are fused

As used herein, the term “bridged polycyclic” refers to compoundswherein the cycloalkyl contains a linkage of one or more atomsconnecting non-adjacent atoms. The following structures

are examples of “bridged” rings. As used herein, the term “spiro” refersto two rings which have one atom in common and the two rings are notlinked by a bridge. Examples of fused cycloalkyl groups aredecahydronaphthalenyl, dodecahydro-1H-phenalenyl andtetradecahydroanthracenyl; examples of bridged cycloalkyl groups arebicyclo[1.1.1]pentyl, adamantanyl, and norbornanyl; and examples ofspiro cycloalkyl groups include spiro[3.3]heptane and spiro [4.5]decane.

The term “cycloalkylene” refers to a cycloalkyl group, as defined above,linking at least two other groups, i.e., a divalent hydrocarbon radical.The two moieties linked to the cycloalkylene can be linked to the sameatom or different atoms of the cycloalkylene. Cycloalkylene groupsinclude, but are not limited to, cyclopropylene, cyclobutylene,cyclopentylene, cyclohexylene, and cyclooctylene.

The term “aryl” refers to a monocyclic or fused bicyclic, tricyclic orgreater, aromatic ring assembly containing 6 to 16 ring carbon atoms.For example, aryl may be phenyl, benzyl or naphthyl, preferably phenyl.Aryl groups can be mono-, di- or tri-substituted by one, two or threeradicals. Preferred as aryl is naphthyl, phenyl or phenyl mono- ordisubstituted by alkoxy, phenyl, halogen, alkyl or trifluoromethyl,especially phenyl or phenyl-mono- or disubstituted by alkoxy, halogen ortrifluoromethyl, and in particular phenyl.

The term “arylene” refers to an aryl group, as defined above, linking atleast two other groups. The two moieties linked to the arylene arelinked to different atoms of the arylene. Arylene groups include, butare not limited to, phenylene.

The term “heteroaryl” refers to a monocyclic or fused bicyclic ortricyclic aromatic ring assembly containing 5 to 16 ring atoms, wherefrom 1 to 4 of the ring atoms are a heteroatom each N, O or S. Forexample, heteroaryl includes pyridyl, indolyl, indazolyl, quinoxalinyl,quinolinyl, isoquinolinyl, benzothienyl, benzofuranyl, furanyl,pyrrolyl, thiazolyl, benzothiazolyl, oxazolyl, isoxazolyl, triazolyl,tetrazolyl, pyrazolyl, imidazolyl, thienyl, or any other radicalssubstituted, especially mono- or di-substituted, by e.g. alkyl, nitro orhalogen. Pyridyl represents 2-, 3- or 4-pyridyl, advantageously 2- or3-pyridyl. Thienyl represents 2- or 3-thienyl. Quinolinyl representspreferably 2-, 3- or 4-quinolinyl. Isoquinolinyl represents preferably1-, 3- or 4-isoquinolinyl. Benzopyranyl, benzothiopyranyl representspreferably 3-benzopyranyl or 3-benzothiopyranyl, respectively. Thiazolylrepresents preferably 2- or 4-thiazolyl, and most preferred 4-thiazolyl.Triazolyl is preferably 1-, 2- or 5-(1,2,4-triazolyl). Tetrazolyl ispreferably 5-tetrazolyl.

Preferably, heteroaryl is pyridyl, indolyl, quinolinyl, pyrrolyl,thiazolyl, isoxazolyl, triazolyl, tetrazolyl, pyrazolyl, imidazolyl,thienyl, furanyl, benzothiazolyl, benzofuranyl, isoquinolinyl,benzothienyl, oxazolyl, indazolyl, or any of the radicals substituted,especially mono- or di-substituted.

The term “heteroalkyl” refers to an alkyl group having from 1 to 3heteroatoms such as N, O and S. The heteroatoms can also be oxidized,such as, but not limited to, —S(O)— and —S(O)₂—. For example,heteroalkyl can include ethers, thioethers, alkyl-amines andalkyl-thiols.

The term “heteroalkylene” refers to a heteroalkyl group, as definedabove, linking at least two other groups. The two moieties linked to theheteroalkylene can be linked to the same atom or different atoms of theheteroalkylene.

The term “heterocycloalkyl” refers to a ring system having from 3 ringmembers to about 20 ring members and from 1 to about 5 heteroatoms suchas N, O and S. The heteroatoms can also be oxidized, such as, but notlimited to, —S(O)— and —S(O)₂—. For example, heterocycle includes, butis not limited to, tetrahydrofuranyl, tetrahydrothiophenyl, morpholino,pyrrolidinyl, pyrrolinyl, imidazolidinyl, imidazolinyl, pyrazolidinyl,pyrazolinyl, piperazinyl, piperidinyl, indolinyl, quinuclidinyl and1,4-dioxa-8-aza-spiro[4.5]dec-8-yl.

The term “heterocycloalkylene” refers to a heterocyclalkyl group, asdefined above, linking at least two other groups. The two moietieslinked to the heterocycloalkylene can be linked to the same atom ordifferent atoms of the heterocycloalkylene.

The term “optionally substituted” is used herein to indicate a moietythat can be unsubstituted or substituted by one or more substituent.When a moiety term is used without specifically indicating assubstituted, the moiety is unsubstituted.

Description

To overcome the current obstacles associated with developing high-energyfull-cells with Si-based anodes, the next generation of oxidation-stableelectrolytes or electrolyte additives are developed. The electrolyte orelectrolyte additives can form a stable, electronically insulating butionically conducting SEI layer on the surface of Si anodes.Additionally, these electrolytes or additives may also help modifycathode surfaces, forming stable CEI layers. These could enable theelectrochemical stability of Li-ion batteries when cycled at highervoltages and help with calendar life of the batteries. In addition, toalleviate battery safety concerns, these additives may impart anincreased thermal stability to the organic components of theelectrolyte, drive a rise in the flash point of the electrolyteformulations, increase the flame-retardant effectiveness and enhancethermal stability of SEI or CEI layers on the surface of electrodes.

In the present disclosure, the use of chemical compounds comprisingether electrolyte additives for energy storage devices with Si-dominantanodes are described. Due to their unique chemical structures andfunctional groups, ether containing electrolyte additives may bring thefollowing benefits: (i) stabilize solid/electrolyte interface film toreduce electrolyte reactions (oxidation on the NCM or NCA cathode andreduction on the Si anode), prevent Si anode volume expansion, andprotect transition metal ion dissolution from NCM cathode; and (ii)reduce the flammability and enhance the thermal stability of organicelectrolytes and increase the safety of electrolyte solutions. Due totheir versatility in reaction chemistry and overall stability inelectrochemical environments, as well as have excellent flame resistanceor fire retardant properties, involving ether containing electrolyteadditives into electrolyte solutions may help improve both overallelectrochemical performance and safety of Si anode-based Li-ionbatteries.

Typical carbon anode electrodes include a current collector such as acopper sheet. Carbon is deposited onto the collector along with aninactive binder material. Carbon is often used because it has excellentelectrochemical properties and is also electrically conductive. If thecurrent collector layer (e.g., copper layer) was removed, the carbonwould likely be unable to mechanically support itself. Therefore,conventional electrodes require a support structure such as thecollector to be able to function as an electrode. The electrode (e.g.,anode or cathode) compositions described in this application can produceelectrodes that are self-supported. The need for a metal foil currentcollector is eliminated or minimized because conductive carbonizedpolymer is used for current collection in the anode structure as well asfor mechanical support. In typical applications for the mobile industry,a metal current collector is typically added to ensure sufficient rateperformance. The carbonized polymer can form a substantially continuousconductive carbon phase in the entire electrode as opposed toparticulate carbon suspended in a non-conductive binder in one class ofconventional lithium-ion battery electrodes. Advantages of a carboncomposite blend that utilizes a carbonized polymer can include, forexample, 1) higher capacity, 2) enhanced overcharge/dischargeprotection, 3) lower irreversible capacity due to the elimination (orminimization) of metal foil current collectors, and 4) potential costsavings due to simpler manufacturing.

Anode electrodes currently used in the rechargeable lithium-ion cellstypically have a specific capacity of approximately 200 milliamp hoursper gram (including the metal foil current collector, conductiveadditives, and binder material). Graphite, the active material used inmost lithium ion battery anodes, has a theoretical energy density of 372milliamp hours per gram (mAh/g). In comparison, silicon has a hightheoretical capacity of 4200 mAh/g. In order to increase volumetric andgravimetric energy density of lithium-ion batteries, silicon may be usedas the active material for the cathode or anode. Several types ofsilicon materials, e.g., silicon nanopowders, silicon nanofibers, poroussilicon, and ball-milled silicon, have also been reported as viablecandidates as active materials for the negative or positive electrodes.Small particle sizes (for example, sizes in the nanometer range)generally can increase cycle life performance. They also can displayvery high initial irreversible capacity. However, small particle sizesalso can result in very low volumetric energy density (for example, forthe overall cell stack) due to the difficulty of packing the activematerial. Larger particle sizes, (for example, sizes in the micronrange) generally can result in higher density anode material. However,the expansion of the silicon active material can result in poor cyclelife due to particle cracking. For example, silicon can swell in excessof 300% upon lithium insertion. Because of this expansion, anodesincluding silicon should be allowed to expand while maintainingelectrical contact between the silicon particles.

Cathode electrodes described herein may include metal oxide cathodematerials, such as Lithium Cobalt Oxide (LiCoO₂) (LCO), Ni-rich oxides,high voltage cathode materials, lithium rich oxides, nickel-rich layeredoxides, lithium rich layered oxides, high-voltage spinel oxides, andhigh-voltage polyanionic compounds. Ni-rich oxides and/or high voltagecathode materials may include NCM and NCA. One example NCM materialincludes LiNi_(0.6)Co_(0.2)Mn_(0.2)O₂ (NCM-622). Lithium rich oxides mayinclude xLi₂Mn₃O₂.(1−x)LiNi_(a)Co_(b)Mn_(c)O₂. Nickel-rich layeredoxides may include LiNi_(1+x)M_(1−x)O_(z) (where M=Co, Mn or Al).Lithium rich layered oxides may include LiNi_(1+x)M_(1−x)O₂ (where M=Co,Mn or Ni). High-voltage spinel oxides may include LiNi_(0.5)Mn_(1.5)O₄.High-voltage polyanionic compounds may include phosphates, sulfates,silicates, etc.

As described herein and in U.S. patent application Ser. No. 13/008,800and Ser. No. 13/601,976, entitled “Composite Materials forElectrochemical Storage” and “Silicon Particles for Battery Electrodes,”respectively, certain embodiments utilize a method of creatingmonolithic, self-supported anodes using a carbonized polymer. Becausethe polymer is converted into an electrically conductive andelectrochemically active matrix, the resulting electrode is conductiveenough that, in some embodiments, a metal foil or mesh current collectorcan be omitted or minimized. The converted polymer also acts as anexpansion buffer for silicon particles during cycling so that a highcycle life can be achieved. In certain embodiments, the resultingelectrode is an electrode that is comprised substantially of activematerial. In further embodiments, the resulting electrode issubstantially active material. The electrodes can have a high energydensity of between about 500 mAh/g to about 1200 mAh/g that can be dueto, for example, 1) the use of silicon, 2) elimination or substantialreduction of metal current collectors, and 3) being comprised entirelyor substantially entirely of active material.

As described herein and in U.S. patent application Ser. No. 14/800,380,entitled “Electrolyte Compositions for Batteries,” the entirety of whichis hereby incorporated by reference, composite materials can be used asan anode in most conventional Li-ion batteries; they may also be used asthe cathode in some electrochemical couples with additional additives.The composite materials can also be used in either secondary batteries(e.g., rechargeable) or primary batteries (e.g., non-rechargeable). Insome embodiments, the composite materials can be used in batteriesimplemented as a pouch cell, as described in further details herein. Incertain embodiments, the composite materials are self-supportedstructures. In further embodiments, the composite materials areself-supported monolithic structures. For example, a collector may beincluded in the electrode comprised of the composite material. Incertain embodiments, the composite material can be used to form carbonstructures discussed in U.S. patent application Ser. No. 12/838,368entitled “Carbon Electrode Structures for Batteries,” the entirety ofwhich is hereby incorporated by reference. Furthermore, the compositematerials described herein can be, for example, silicon compositematerials, carbon composite materials, and/or silicon-carbon compositematerials.

In some embodiments, a largest dimension of the silicon particles can beless than about 40 μm, less than about 1 μm, between about 10 nm andabout 40 μm, between about 10 nm and about 1 μm, less than about 500 nm,less than about 100 nm, and about 100 nm. All, substantially all, or atleast some of the silicon particles may comprise the largest dimensiondescribed above. For example, an average or median largest dimension ofthe silicon particles can be less than about 40 μmm, less than about 1μm, between about 10 nm and about 40 μmm, between about 10 nm and about1 μm, less than about 500 nm, less than about 100 nm, and about 100 nm.The amount of silicon in the composite material can be greater than zeropercent by weight of the mixture and composite material. In certainembodiments, the mixture comprises an amount of silicon, the amountbeing within a range of from about 0% to about 90% by weight, includingfrom about 30% to about 80% by weight of the mixture. The amount ofsilicon in the composite material can be within a range of from about 0%to about 35% by weight, including from about 0% to about 25% by weight,from about 10% to about 35% by weight, and about 20% by weight. Infurther certain embodiments, the amount of silicon in the mixture is atleast about 30% by weight. Additional embodiments of the amount ofsilicon in the composite material include more than about 50% by weight,between about 30% and about 80% by weight, between about 50% and about70% by weight, and between about 60% and about 80% by weight.Furthermore, the silicon particles may or may not be pure silicon. Forexample, the silicon particles may be substantially silicon or may be asilicon alloy. In one embodiment, the silicon alloy includes silicon asthe primary constituent along with one or more other elements.

As described herein, micron-sized silicon particles can provide goodvolumetric and gravimetric energy density combined with good cycle life.In certain embodiments, to obtain the benefits of both micron-sizedsilicon particles (e.g., high energy density) and nanometer-sizedsilicon particles (e.g., good cycle behavior), silicon particles canhave an average particle size in the micron range and a surfaceincluding nanometer-sized features. In some embodiments, the siliconparticles have an average particle size (e.g., average diameter oraverage largest dimension) between about 0.1 μmm and about 30 μmm orbetween about 0.1 μmm and all values up to about 30 μmm. For example,the silicon particles can have an average particle size between about0.5 μmm and about 25 μmm, between about 0.5 μmm and about 20 μmm,between about 0.5 μmm and about 15 μmm, between about 0.5 μmm and about10 μmm, between about 0.5 μmm and about 5μm, between about 0.5 μmm andabout 2 μm, between about 1 μm and about 20 μmm, between about 1 μm andabout 15 μmm, between about 1 μmm and about 10 μmm, between about 5 μmand about 20 μmm, etc. Thus, the average particle size can be any valuebetween about 0.1 μmm and about 30 μmm, e.g., 0.1 μmm, 0.5 μmm, 1 μm, 5μmm, 10 μmm, 15 μmm, 20 μmm, 25 μmm, and 30 μmm.

The composite material can be formed by pyrolyzing a polymer precursor,such as polyamide acid. The amount of carbon obtained from the precursorcan be about 50 weight percent by weight of the composite material. Incertain embodiments, the amount of carbon from the precursor in thecomposite material is about 10% to about 25% by weight. The carbon fromthe precursor can be hard carbon. Hard carbon can be a carbon that doesnot convert into graphite even with heating in excess of 2800 degreesCelsius. Precursors that melt or flow during pyrolysis convert into softcarbons and/or graphite with sufficient temperature and/or pressure.Hard carbon may be selected since soft carbon precursors may flow andsoft carbons and graphite are mechanically weaker than hard carbons.Other possible hard carbon precursors can include phenolic resins, epoxyresins, and other polymers that have a very high melting point or arecrosslinked. In some embodiments, the amount of hard carbon in thecomposite material has a value within a range of from about 10% to about25% by weight, about 20% by weight, or more than about 50% by weight. Incertain embodiments, the hard carbon phase is substantially amorphous.In other embodiments, the hard carbon phase is substantiallycrystalline. In further embodiments, the hard carbon phase includesamorphous and crystalline carbon. The hard carbon phase can be a matrixphase in the composite material. The hard carbon can also be embedded inthe pores of the additives including silicon. The hard carbon may reactwith some of the additives to create some materials at interfaces. Forexample, there may be a silicon carbide layer between silicon particlesand the hard carbon.

In certain embodiments, graphite particles are added to the mixture.Advantageously, graphite can be an electrochemically active material inthe battery as well as an elastic deformable material that can respondto volume change of the silicon particles. Graphite is the preferredactive anode material for certain classes of lithium-ion batteriescurrently on the market because it has a low irreversible capacity.Additionally, graphite is softer than hard carbon and can better absorbthe volume expansion of silicon additives. In certain embodiments, alargest dimension of the graphite particles is between about 0.5 micronsand about 20 microns. All, substantially all, or at least some of thegraphite particles may comprise the largest dimension described herein.In further embodiments, an average or median largest dimension of thegraphite particles is between about 0.5 microns and about 20 microns. Incertain embodiments, the mixture includes greater than 0% and less thanabout 80% by weight of graphite particles. In further embodiments, thecomposite material includes about 40% to about 75% by weight graphiteparticles.

In certain embodiments, conductive particles which may also beelectrochemically active are added to the mixture. Such particles canenable both a more electronically conductive composite as well as a moremechanically deformable composite capable of absorbing the largevolumetric change incurred during lithiation and de-lithiation. Incertain embodiments, a largest dimension of the conductive particles isbetween about 10 nanometers and about 7 millimeters. All, substantiallyall, or at least some of the conductive particles may comprise thelargest dimension described herein. In further embodiments, an averageor median largest dimension of the conductive particles is between about10 nm and about 7 millimeters. In certain embodiments, the mixtureincludes greater than zero and up to about 80% by weight conductiveparticles. In further embodiments, the composite material includes about45% to about 80% by weight conductive particles. The conductiveparticles can be conductive carbon including carbon blacks, carbonfibers, carbon nanofibers, carbon nanotubes, graphite, graphene, etc.Many carbons that are considered as conductive additives that are notelectrochemically active become active once pyrolyzed in a polymermatrix. Alternatively, the conductive particles can be metals or alloysincluding copper, nickel, or stainless steel.

The composite material may also be formed into a powder. For example,the composite material can be ground into a powder. The compositematerial powder can be used as an active material for an electrode. Forexample, the composite material powder can be deposited on a collectorin a manner similar to making a conventional electrode structure, asknown in the industry.

In some embodiments, the full capacity of the composite material may notbe utilized during use of the battery to improve battery life (e.g.,number charge and discharge cycles before the battery fails or theperformance of the battery decreases below a usability level). Forexample, a composite material with about 70% by weight siliconparticles, about 20% by weight carbon from a precursor, and about 10% byweight graphite may have a maximum gravimetric capacity of about 2000mAh/g, while the composite material may only be used up to a gravimetriccapacity of about 550 to about 850 mAh/g. Although, the maximumgravimetric capacity of the composite material may not be utilized,using the composite material at a lower capacity can still achieve ahigher capacity than certain lithium ion batteries. In certainembodiments, the composite material is used or only used at agravimetric capacity below about 70% of the composite material's maximumgravimetric capacity. For example, the composite material is not used ata gravimetric capacity above about 70% of the composite material'smaximum gravimetric capacity. In further embodiments, the compositematerial is used or only used at a gravimetric capacity below about 50%of the composite material's maximum gravimetric capacity or below about30% of the composite material's maximum gravimetric capacity.

Electrolyte

An electrolyte for a lithium ion battery can include a solvent and alithium ion source, such as a lithium-containing salt. The compositionof the electrolyte may be selected to provide a lithium ion battery withimproved performance. In some embodiments, the electrolyte may containan electrolyte additive. As described herein, a lithium ion battery mayinclude a first electrode, a second electrode, a separator between thefirst electrode and the second electrode, and an electrolyte in contactwith the first electrode, the second electrode, and the separator. Theelectrolyte serves to facilitate ionic transport between the firstelectrode and the second electrode. In some embodiments, the firstelectrode and the second electrode can refer to anode and cathode orcathode and anode, respectively.

In some embodiments, the electrolyte for a lithium ion battery mayinclude a solvent comprising a fluorine-containing component, such as afluorine-containing cyclic carbonate, a fluorine-containing linearcarbonate, and/or a fluoroether. In some embodiments, the electrolytecan include more than one solvent. For example, the electrolyte mayinclude two or more co-solvents. In some embodiments, at least one ofthe co-solvents in the electrolyte is a fluorine-containing compound. Insome embodiments, the fluorine-containing compound may be fluoroethylenecarbonate (FEC), 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropylether, or difluoroethylene carbonate (F2EC). In some embodiments, theco-solvent may be selected from the group consisting of FEC, ethylmethyl carbonate (EMC), 1,1,2,2-tetrafluoroethyl2,2,3,3-tetrafluoropropyl ether, difluoroethylene carbonate (F2EC),ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate(DMC), propylene carbonate (PC), and gamma-Butyrolactone (GBL). In someembodiments, the electrolyte contains FEC. In some embodiments, theelectrolyte contains both EMC and FEC. In some embodiments, theelectrolyte may further contain 1,1,2,2-tetrafluoroethyl2,2,3,3-tetrafluoropropyl ether, EC, DEC, DMC, PC, GBL, and/or F2EC orsome partially or fully fluorinated linear or cyclic carbonates, ethers,etc. as a co-solvent. In some embodiments, the electrolyte is free orsubstantially free of non-fluorine-containing cyclic carbonates, such asEC, GBL, and PC.

As used herein, a co-solvent of an electrolyte has a concentration of atleast about 10% by volume (vol %). In some embodiments, a co-solvent ofthe electrolyte may be about 20 vol %, about 40 vol %, about 60 vol %,or about 80 vol %, or about 90 vol % of the electrolyte. In someembodiments, a co-solvent may have a concentration from about 10 vol %to about 90 vol %, from about 10 vol % to about 80 vol %, from about 10vol % to about 60 vol %, from about 20 vol % to about 60 vol %, fromabout 20 vol % to about 50 vol %, from about 30 vol % to about 60 vol %,or from about 30 vol % to about 50 vol %.

For example, in some embodiments, the electrolyte may contain afluorine-containing cyclic carbonate, such as FEC, at a concentration ofabout 10 vol % to about 60 vol %, including from about 20 vol % to about50 vol %, and from about 20 vol % to about 40 vol %. In someembodiments, the electrolyte may comprise a linear carbonate that doesnot contain flourine, such as EMC, at a concentration of about 40 vol %to about 90 vol %, including from about 50 vol % to about 80 vol %, andfrom about 60 vol % to about 80 vol %. In some embodiments, theelectrolyte may comprise 1,1,2,2-tetrafluoroethyl2,2,3,3-tetrafluoropropyl ether at a concentration of from about 10 vol% to about 30 vol %, including from about 10 vol % to about 20 vol %.

In some embodiments, the electrolyte is substantially free of cycliccarbonates other than fluorine-containing cyclic carbonates (i.e.,non-fluorine-containing cyclic carbonates). Examples ofnon-fluorine-containing carbonates include EC, PC, GBL, and vinylenecarbonate (VC).

Electrolyte Additives

In some embodiments, the electrolyte may further comprise one or moreadditives. As used herein, an additive of the electrolyte refers to acomponent that makes up less than 10% by weight (wt %) of theelectrolyte. In some embodiments, the amount of each additive in theelectrolyte may be from about 0.2 wt % to about 1 wt %, 0.1 wt % toabout 2 wt %, 0.2 wt % to about 9 wt %, from about 0.5 wt % to about 9wt %, from about 1 wt % to about 9 wt %, from about 1 wt % to about 8 wt%, from about 1 wt % to about 8 wt %, from about 1 wt % to about 7 wt %,from about 1 wt % to about 6 wt %, from about 1 wt % to about 5 wt %,from about 2 wt % to about 5 wt %, or any value in between. In someembodiments, the total amount of the additive(s) may be from about 1 wt% to about 9 wt %, from about 1 wt % to about 8 wt %, from about 1 wt %to about 7 wt %, from about 2 wt % to about 7 wt %, or any value inbetween.

Ether Compounds

In some embodiments, the electrolyte may further comprise one or more ofthe compounds selected from Formula (A):

wherein R₁ and R₂ are each independently selected from C1-C6 alkyl,C1-C8 heteroalkly with at least one heteroatom O, C2-C6 alkenyl,alkynyl, C2-C12 heteroalkenly with at least one heteroatom O. In someembodiments, R₁ and R₂ are each independently selected from the groupconsisting of C1-C6 alkyl,

wherein n is an integer selected from 1-6, and p is an integer selectedfrom 1-3.

In some embodiments, the electrolyte may further comprise one or more ofthe compounds selected from Formula (B):

wherein R₃, R₄, and R₅ are each independently selected from C2-C4alkenyl; and A is C1-C6 alkyl. In some embodiments, R₃, R₄, and R₅ areeach independently

In some embodiments, the electrolyte may further comprise one or more ofthe compounds selected from Formula (C):

wherein R₆, R₇, R₈, and R₉ are each independently selected from C2-C4alkenyl; and B is C1-C6 alkyl. In some embodiments, R₆, R₇, R₈, and R₉are each independently

In some embodiments, the electrolyte may further comprise one or more ofthe compounds selected from Formula (D):

wherein R₁₀, R₁₁, R₁₂, R₁₃, R₁₄, and R₁₅ are each independently selectedfrom C2-C4 alkenyl; C and D are each independently C1-C6 alkyl; and

In some embodiments, R₁₀, R₁₁, R₁₂, R₁₃, R₁₄, and R₁₅ are eachindependently

The electrolyte or additive may comprise an ether compound. In someembodiments, the additive may be an additive chemical compoundcomprising an ether compound as defined herein. In some embodiments, theether compound is used as an additive along with LiF. In someembodiments, the ether compound may be included in the electrolyte as aco-solvent. In other embodiments, the ether compound may be included inthe electrolyte as an additive. For example, the electrolyte may containan ether compound as a co-solvent at a concentration of about 10 vol %or more. In other embodiments, the electrolyte may contain an ethercompound as an additive at less than 10 weight %.

In some embodiments, the ether compound include allyl ethers and theirderivatives, diallyl ethers and their derivative, triallyl ethers andtheir derivatives; and tetraallyl ethers and their derivatives. In someembodiments, the ether compound is selected from allyl ether;1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether;1-(2-methoxyethoxy)butane; 2,5,8,11-tetraoxadodecane;2,5,8,11,14-pentaoxapentadecane; 3-(prop-2-enoxymethoxy)prop-1-ene;Ethylene glycol diallyl ether; 1,4-Butanediol divinyl ether;Tri(ethylene glycol) divinyl ether; Di(ethylene glycol) divinyl ether;Triallyl orthoformate; 1,2,3-tris(prop-2-enoxy)propane; PentaerythritolTriallyl Ether, 1-prop-2-enoxy-2,2-bis(prop-2-enoxymethyl)butane;1,3-bis(prop-2-enoxy)-2,2-bis(prop-2-enoxymethyl)propane;Tetrakis(vinyloxymethyl)methane;Bis[3-prop-2-enoxy-2,2-bis(prop-2-enoxymethyl)propyl] but-2-enedioate;and Glyoxal bis(diallyl acetal); 1,1,3,3-Tetraallyloxypropane.

Example structures of ether compounds and are shown below:

1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (D2)

1-(2-methoxyethoxy)butane (G2)

2,5,8,11-tetraoxadodecane (G3)

2,5,8,11,14- pentaoxapentadecane (G4)

Ethylene glycol diallyl ether

1,4-Butanediol divinyl ether

Tri(ethylene glycol) divinyl ether

Di(ethylene glycol) divinyl ether

Triallyl orthoformate

1,2,3-tris(prop-2- enoxy)propane

Pentaerythritol Triallyl Ether

1-prop-2-enoxy-2,2- bis(prop-2- enoxymethyl)butane

1,3-bis(prop-2-enoxy)-2,2- bis(prop-2- enoxymethyl)propane

Tetrakis(vinyloxymethyl) methane

Bis[3-prop-2-enoxy-2,2- bis(prop-2- enoxymethyl)propyl]but-2- enedioate

Glyoxal bis(diallyl acetal)

1,1,3,3- Tetraallyloxypropane

In some embodiments, a lithium-containing salt for a lithium ion batterymay comprise lithium hexafluorophosphate (LiPF₆). In some embodiments, alithium-containing salt for a lithium ion battery may comprise one ormore of lithium tetrafluoroborate (LiBF₄), lithium hexafluoroarsenatemonohydrate (LiAsF₆), lithium perchlorate (LiClO₄), lithiumbis(trifluoromethanesulfonyl)imide (LiTFSI), lithiumbis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalato)borate (LiBOB),lithium difluoro(oxalate)borate (LiDFOB), lithium triflate (LiCF₃SO₃),lithium tetrafluorooxalato phosphate (LTFOP), lithium difluorophosphate(LiPO₂F₂), lithium pentafluoroethyltrifluoroborate (LiFAB), and lithium2-trifluoromethyl-4,5-dicyanoimidazole (LiTDI), etc. In someembodiments, the electrolyte can have a salt concentration of about 1moles/L (M).

These electrolyte additives, along with the electrolytes, can be reducedor self-polymerize on the surface of Si anode to form a SEI layer thatcan reduce or prevent the crack and/or the continuous reduction ofelectrolyte solutions as the silicon containing anode expands andcontracts during cycling. Furthermore, these electrolyte additives,along with the electrolyte solvents, may be oxidized on a cathodesurface to form a CEI layer that can suppress or minimize furtherdecomposition of the electrolyte on the surface of the cathode. Withoutbeing bound to the theory or mode of operation, it is believed that thepresence of ether in the electrolyte can result in a SEI and/or CEIlayer on the surface of electrodes with improved performance. An SEIlayer comprising an ether compound may demonstrate improved chemicalstability and increased density, for example, compared to SEI layersformed by electrolytes without additives or with traditional additives.As such, the change in thickness and surface reactivity of the interfacelayer are limited, which may in turn facilitate reduction in capacityfade and/or generation of excessive gaseous byproducts during operationof the lithium ion battery. A CEI layer comprising an ether compound maydemonstrate may help minimize the transition metal ion dissolutions andstructure changes on cathode side and may provide favorable kineticsresulting in improved cycling stability and rate capability. In someembodiments, electrolyte solvents comprising an ether compound may beless flammable and more flame retardant.

In addition, the presence of LiF in solution can have an impact oncycling ability by modifying the SEI structure because of itspreponderance within the SEI. However, the salt precipitation on the SEImay have a negative effect on the SEI formation. An ether additive mayreduce the effect of LiF on the battery performances by complexing withLiF, which prevents LiF aggregation and precipitation on SEI film. Atthe same time, it does not inhibit in any way the availability andtransportation of Li-ions from LiPF₆ salt. In some embodiments, when anether compound is combined with LiF as bi-component additives forSi-dominant anodes in Li-ion batteries, the ether compound may chelatewith LiF and make them homogeneously disperse among Si-anode/electrolyteinterphase. These will help reduce the Li-ion loss from cathode sides.In addition, the formed complexes are electrochemically stable. Theirhigh oxidation potential allows using them in batteries withhigh-voltage cathodes.

These bi-component-based complexes should be more stable and are muchless prone to be reduced by a radical attack in reductive environmentson the surface of Si anodes. This will significantly decrease the SEIgrowth rate. The novel bi-component additive-based new electrolytescould modify the SEI layer composition and improve the SEI stability,which permits effective surface passivation of the anode, increase SEIrobustness and structural stability on the silicon-dominant anodes.Other desired effects include improving the mechanical properties of theSEI, increasing the ratio of organic components to inorganic componentsin the SEI, and/or improving the uniformity, flexibility and elasticityof the SEI. This will help avoid the parasitic reactions occurred on thesurface of cathode, leading to minimized electrolyte decomposition,minimized loss of active Li and impedance rise on theelectrode/electrolyte interface. Through the formation of a stable SEIlayer and passivation layer on the surfaces of Si-dominant anodes, thebatteries containing these bi-component-based additives (in electrolyte)should have higher Coulombic efficiency and longer cycle life than thecontrol ones.

In some embodiments, a lithium ion battery comprising an electrolytecomposition according to one or more embodiments described herein, andan anode having a composite electrode film according to one or moreembodiments described herein, may demonstrate reduced gassing and/orswelling at about room temperature (e.g., about 20° C. to about 25° C.)or elevated temperatures (e.g., up to temperatures of about 85° C.),increased cycle life at about room temperature or elevated temperatures,and/or reduced cell growth/electrolyte consumption per cycle, forexample compared to lithium ion batteries comprising conventionallyavailable electrolyte compositions in combination with an anode having acomposite electrode film according to one or more embodiments describedherein. In some embodiments, a lithium ion battery comprising anelectrolyte composition according to one or more embodiments describedherein and an anode having a composite electrode film according to oneor more embodiments described herein may demonstrate reduced gassingand/or swelling across various temperatures at which the battery may besubject to testing, such as temperatures between about −20° C. and about130° C. (e.g., compared to lithium ion batteries comprisingconventionally available electrolyte compositions in combination with ananode having a composite electrode film according to one or moreembodiments described herein).

Gaseous byproducts may be undesirably generated during batteryoperation, for example, due to chemical reactions between theelectrolyte and one or more other components of the lithium ion battery,such as one or more components of a battery electrode. Excessive gasgeneration during operation of the lithium ion battery may adverselyaffect battery performance and/or result in mechanical and/or electricalfailure of the battery. For example, undesired chemical reactionsbetween an electrolyte and one or more components of an anode may resultin gas generation at levels which can mechanically (e.g., structuraldeformation) and/or electrochemically degrade the battery. In someembodiments, the composition of the anode and the composition of theelectrolyte can be selected to facilitate desired gas generation.

Energy Storage Device

The electrolytes and electrolyte additives described herein may beadvantageously utilized within an energy storage device. In someembodiments, energy storage devices may include batteries, capacitors,and battery-capacitor hybrids. In some embodiments, the energy storagedevice comprise lithium. In some embodiments, the energy storage devicemay comprise at least one electrode, such as an anode and/or cathode. Insome embodiments, at least one electrode may be a Si-based electrode. Insome embodiments, the Si-based electrode is a Si-dominant electrode,where silicon is the majority of the active material used in theelectrode (e.g., greater than 50% silicon). In some embodiments, theenergy storage device comprises a separator. In some embodiments, theseparator is between a first electrode and a second electrode.

In some embodiments, the energy storage device comprises an electrolyte.In some embodiments, the electrolyte comprises a solvent, solventadditive and/or compound as described previously herein. For example, insome embodiments, the electrolyte comprises a cyclic organosiliconcompound as described previously herein.

Pouch Cell

As described herein, a battery can be implement as a pouch cell. FIG. 1shows a cross-sectional schematic diagram of an example of a lithium ionbattery 300 implemented as a pouch cell, according to some embodiments.The battery 300 comprises an anode 316 in contact with a negativecurrent collector 308, a cathode 304 in contact with a positive currentcollector 310, a separator 306 disposed between the anode 316 and thecathode 304. In some embodiments, a plurality of anodes 316 and cathode304 may be arranged into a stacked configuration with a separator 306separating each anode 316 and cathode 304. Each negative currentcollector 308 may have one anode 316 attached to each side; eachpositive current collector 310 may have one cathode 304 attached to eachside. The stacks are immersed in an electrolyte 314 and enclosed in apouch 312. The anode 302 and the cathode 304 may comprise one or morerespective electrode films formed thereon. The number of electrodes ofthe battery 300 may be selected to provide desired device performance.

With further reference to FIG. 1, the separator 306 may comprise asingle continuous or substantially continuous sheet, which can beinterleaved between adjacent electrodes of the electrode stack. Forexample, the separator 306 may be shaped and/or dimensioned such that itcan be positioned between adjacent electrodes in the electrode stack toprovide desired separation between the adjacent electrodes of thebattery 300. The separator 306 may be configured to facilitateelectrical insulation between the anode 302 and the cathode 304, whilepermitting ionic transport between the anode 302 and the cathode 304. Insome embodiments, the separator 306 may comprise a porous material,including a porous polyolefin material.

The lithium ion battery 300 may include an electrolyte 314, for examplean electrolyte having a composition as described herein. The electrolyte314 is in contact with the anode 302, the cathode 304, and the separator306.

With continued reference to FIG. 1, the anode 302, cathode 304 andseparator 306 of the lithium ion battery 300 may be enclosed in ahousing comprising a pouch 312. In some embodiments, the pouch 312 maycomprise a flexible material. For example, the pouch 312 may readilydeform upon application of pressure on the pouch 312, including pressureexerted upon the pouch 312 from within the housing. In some embodiments,the pouch 312 may comprise aluminum. For example, the pouch 312 maycomprise a laminated aluminum pouch.

In some embodiments, the lithium ion battery 300 may comprise an anodeconnector (not shown) and a cathode connector (not shown) configured toelectrically couple the anodes and the cathodes of the electrode stackto an external circuit, respectively. The anode connector and a cathodeconnector may be affixed to the pouch 312 to facilitate electricalcoupling of the battery 300 to an external circuit. The anode connectorand the cathode connector may be affixed to the pouch 312 along one edgeof the pouch 312. The anode connector and the cathode connector can beelectrically insulated from one another, and from the pouch 312. Forexample, at least a portion of each of the anode connector and thecathode connector can be within an electrically insulating sleeve suchthat the connectors can be electrically insulated from one another andfrom the pouch 312.

EXAMPLES

The below example devices and processes for device fabrication generallydescribed below, and the performances of lithium ion batteries withdifferent electrolytes and electrolyte additives are evaluated.

Example 1

In Example 1, 0.1M 1-(2-methoxyethoxy)butane (G2) & LiF was used aselectrolyte additives and added to and added to 1.2M LiPF₆ in FEC/EMC(3/7 wt %)-based electrolytes for Si-dominant anode//LiCoO₂ cathode full5 layer pouch cells, and compared to a control without an electrolyteadditive. The electrochemical tests were carried out at 1 C/0.5 Ccharge/discharge processes with the working voltage of 4.3V-3.3 V.

In FIGS. 2A-4B, the electrolytes used were: 1) A Control with 1.2 MLiPF₆ in FEC/EMC (3/7 wt %) (shown as a dotted line); and 2) 1 M LiPF₆in FEC/EMC (3/7 wt %) +0.1M G2 & LiF (shown as a solid line). TheSi-dominant anodes contain about 80 wt % Si, 5 wt % graphite and 15 wt %glass carbon (from resin), and are laminated on 15 μm Cu foil. Theaverage loading is about 3.8 mg/cm². The cathodes contain about 97 wt %LiCoO₂, 1 wt % Super P and 2 wt % PVDF5130, and are laminated on 15 μmAl foil. The average loading is about 28 mg/cm².

FIGS. 2A and 2B show the Capacity (A) and capacity retention ofSi-dominant anode//LiCoO₂ cathode full cells, respectively, wherecontrol cells and cells containing 0.1M G2 & LiF additive were tested.The long-term cycling for both control and 0.1M G2 & LiFadditive-containing cells include: (i) At the 1^(st) cycle, charge at0.5 C to 4.3 V for 5 hours, rest 5 minutes, 1 ms IR, 100 ms IR,discharge at 0.2 C to 2.75 V, rest 5 minutes, 1 ms IR, 100 ms IR; and(ii) from the 2^(nd) cycle, charge at 1 C to 4.3 V until 0.05 C, rest 5minutes, 1 ms IR, 100 ms IR, discharge at 0.5 to 3.3 V, rest 5 minutes,1 ms IR, 100 ms IR. But after each 49 cycles, the test conditions in the1^(st) cycle were repeated.

In addition, both control and 0.1M G2 & LiF-containing cells wereformatted for 6 cycles at the following conditions before long-termcycling: (i) At the 1^(st) cycle, Rest 5 minutes, charge at 0.025 C to25% nominal capacity, charge at 0.2 C to 4.3 V until 0.05 C, rest 5minutes, discharge at 0.2 C to 3.3 V, rest 5 minutes; and (ii) from2^(nd) to 6^(th) cycles, charge at 0.5 C to 4.3 V until 0.05 C, rest 5minutes, discharge at 0.5 C to 3.3 V, rest 5 minutes. FIGS. 2A and 2Bindicate that when adding 0.1M G2 & LiF bi-component additive into 1.2 MLiPF₆ in FEC/EMC (3/7 wt %)-based electrolytes, the cell capacityretention is improved.

FIGS. 3A and 3B show average resistance during 10 sec pulse for thecharge (A) and discharge (B) processes of Si-dominant anode//LiCoO₂cathode full cell, respectively, where control cells and cellscontaining 0.1M G2 & LiF were tested. The long-term cycling for bothcontrol and 0.1M G2 & LiF additive-containing cells include: (i) At the1^(st) cycle, charge at 0.5 C to 4.3 V for 5 hours, rest 5 minutes, 1 msIR, 100 ms IR, discharge at 0.2 C to 2.75 V, rest 5 minutes, 1 ms IR,100 ms IR; and (ii) from the 2^(nd) cycle, charge at 1 C to 4.3 V until0.05 C, rest 5 minutes, 1 ms IR, 100 ms IR, discharge at 0.5 C to 3.3 V,rest 5 minutes, 1 ms IR, 100 ms IR. But after each 49 cycles, the testconditions in the 1^(st) cycle were repeated.

In addition, both control and 0.1M G2 & LiF-containing cells wereformatted for 6 cycles at the following conditions before long-termcycling: (i) At the 1^(st) cycle, Rest 5 minutes, charge at 0.025 C to25% nominal capacity, charge at 0.2 C to 4.3 V until 0.05 C, rest 5minutes, discharge at 0.2 C to 3.3 V, rest 5 minutes; and (ii) from2^(nd) to 6^(th) cycles, charge at 0.5 C to 4.3 V until 0.05 C, rest 5minutes, discharge at 0.5 C to 3.3 V, rest 5 minutes. The Res fields arevalues calculated using data points of voltage and current. It linearlyinterpolates for a voltage at 10 s or 30 s in the charge/discharge stepbetween the two data points before and after that time. Then it takesthe difference between that voltage and the last voltage during restwhen current is 0 and divides it by the charge or discharge current.Res_10s_C is calculated using discharge data (for the charged state).Res_10s_DC is calculated using charge data (for the cell state at thebeginning of the cycle). The results in FIGS. 3A and 3B show that 0.1MG2 & LiF-containing cells have lower resistance after 10 scharge/discharge processes than control ones after about 200 cycles.

FIGS. 4A and 4B show average resistance during 30 sec pulses for thecharge (A) and discharge (B) processes of Si-dominant anode//LiCoO₂cathode full cells, respectively, where control cells and cellscontaining 0.1M G2 & LiF were tested. The long-term cycling for bothcontrol and 0.1M G2 & LiF additive-containing cells include: (i) At the1^(st) cycle, charge at 0.5 C to 4.3 V for 5 hours, rest 5 minutes, 1 msIR, 100 ms IR, discharge at 0.2 C to 2.75 V, rest 5 minutes, 1 ms IR,100 ms IR; and (ii) from the 2^(nd) cycle, charge at 1 C to 4.3 V until0.05 C, rest 5 minutes, 1 ms IR, 100 ms IR, discharge at 0.5 C to 3.3 V,rest 5 minutes, 1 ms IR, 100 ms IR. But after each 49 cycles, the testconditions in the 1^(st) cycle were repeated.

In addition, both control and 0.1M G2 & LiF-containing cells wereformatted for 6 cycles at the following conditions before long-termcycling: (i) At the 1^(st) cycle, Rest 5 minutes, charge at 0.025 C to25% nominal capacity, charge at 0.2 C to 4.3 V until 0.05 C, rest 5minutes, discharge at 0.2 C to 3.3 V, rest 5 minutes; and (ii) from2^(nd) to 6^(th) cycles, charge at 0.5 C to 4.3 V until 0.05 C, rest 5minutes, discharge at 0.5 C to 3.3 V, rest 5 minutes. The Res fields arevalues calculated using data points of voltage and current. It linearlyinterpolates for a voltage at 10 s or 30 s in the charge/discharge stepbetween the two data points before and after that time. Then it takesthe difference between that voltage and the last voltage during restwhen current is 0 and divides it by the charge or discharge current.Res_30s_C is calculated using discharge data (for the charged state).Res_30s_DC is calculated using charge data (for the cell state at thebeginning of the cycle). The results in FIGS. 4A and 4B show that 0.1MG2 & LiF-containing cells have lower resistance after 30 scharge/discharge processes than control ones after about 200 cycles.

Example 2

In Example 2, 0.05M 2,5,8,11,14-pentaoxapentadecane (G4) & LiF was usedas electrolyte additives and added to and added to 1.2M LiPF₆ in FEC/EMC(3/7 wt %)-based electrolytes for Si-dominant anode//LiCoO₂ cathode full5 layer pouch cells, and compared to a control without an electrolyteadditive. The electrochemical tests were carried out at 1 C/0.5 Ccharge/discharge processes with the working voltage of 4.3V-3.3 V.

In FIGS. 5A and 5B, the electrolytes used were: 1) A Control with 1.2 MLiPF₆ in FEC/EMC (3/7 wt %) (shown as a dotted line); and 2) 1 M LiPF₆in FEC/EMC (3/7 wt %) +0.05M G4 & LiF (shown as a solid line). TheSi-dominant anodes contain about 80 wt % Si, 5 wt % graphite and 15 wt %glass carbon (from resin), and are laminated on 15 μm Cu foil. Theaverage loading is about 3.8 mg/cm². The cathodes contain about 97 wt %LiCoO₂, 1 wt % Super P and 2 wt % PVDF5130, and are laminated on 15 μmAl foil. The average loading is about 28 mg/cm².

FIGS. 5A and 5B show the Capacity (A) and capacity retention ofSi-dominant anode//LiCoO₂ cathode full cells, respectively, wherecontrol cells and cells containing 0.05M G4 & LiF additive were tested.The long-term cycling for both control and 0.05M G4 & LiFadditive-containing cells include: (i) At the 1^(st) cycle, charge at0.5 C to 4.3 V for 5 hours, rest 5 minutes, 1 ms IR, 100 ms IR,discharge at 0.2 C to 2.75 V, rest 5 minutes, 1 ms IR, 100 ms IR; and(ii) from the 2^(nd) cycle, charge at 1 C to 4.3 V until 0.05 C, rest 5minutes, 1 ms IR, 100 ms IR, discharge at 0.5 to 3.3 V, rest 5 minutes,1 ms IR, 100 ms IR. But after each 49 cycles, the test conditions in the1^(st) cycle were repeated.

In addition, both control and 0.05M G4 & LiF-containing cells wereformatted for 6 cycles at the following conditions before long-termcycling: (i) At the 1^(st) cycle, Rest 5 minutes, charge at 0.025 C to25% nominal capacity, charge at 0.2 C to 4.3 V until 0.05 C, rest 5minutes, discharge at 0.2 C to 3.3 V, rest 5 minutes; and (ii) from2^(nd) to 6^(th) cycles, charge at 0.5 C to 4.3 V until 0.05 C, rest 5minutes, discharge at 0.5 C to 3.3 V, rest 5 minutes. FIGS. 5A and 5Bindicates that when adding 0.05M G4 & LiF bi-component additive into 1.2M LiPF₆ in FEC/EMC (3/7 wt %)-based electrolytes, the cell capacityretention is improved after about 200 cycles.

Various embodiments have been described above. Although the inventionhas been described with reference to these specific embodiments, thedescriptions are intended to be illustrative and are not intended to belimiting. Various modifications and applications may occur to thoseskilled in the art without departing from the true spirit and scope ofthe invention as defined in the appended claims.

What is claimed is:
 1. An energy storage device comprising: a firstelectrode and a second electrode, wherein one or both of the firstelectrode and the second electrode is a Si-based electrode; a separatorbetween the first electrode and the second electrode; an electrolyte;and at least one electrolyte additive comprising a compound of Formula(A):

wherein: R₁ and R₂ are each independently selected from C1-C8heteroalkyl with at least one heteroatom O, C2-C6 alkenyl, alkynyl,C2-C12 heteroalkenyl with at least one heteroatom O.
 2. The energystorage device of claim 1, further comprising LiF.
 3. The energy storagedevice of claim 1, wherein the second electrode is a Si-dominantelectrode.
 4. The energy storage device of claim 1, wherein the secondelectrode comprises a composite material.
 5. The energy storage deviceof claim 4, wherein the composite material comprises: greater than 0%and less than about 90% by weight of silicon particles, and greater than0% and less than about 90% by weight of one or more types of carbonphases, wherein at least one of the one or more types of carbon phasesis a substantially continuous phase that holds the composite materialtogether such that the silicon particles are distributed throughout thecomposite material.
 6. The energy storage device of claim 1, wherein theelectrolyte further comprises fluoroethylene carbonate (FEC).
 7. Theenergy storage device of claim 6, wherein the electrolyte issubstantially free of non-fluorine containing cyclic carbonate.